U.S. patent number 6,925,132 [Application Number 10/136,307] was granted by the patent office on 2005-08-02 for method for detecting and correcting amplitude and phase imbalances between i and q components in quadrature demodulator.
This patent grant is currently assigned to Electronics and Telecommunications Research Institute. Invention is credited to Nae-Soo Kim, Young-Wan Kim, Ho-Jin Lee, Yun-Jeong Song.
United States Patent |
6,925,132 |
Song , et al. |
August 2, 2005 |
Method for detecting and correcting amplitude and phase imbalances
between I and Q components in quadrature demodulator
Abstract
Disclosed is a method for detecting and correcting amplitude and
phase imbalances between in-phase (I) and quadrature-phase (Q)
components in a high-speed wireless communication quadrature
demodulator, which comprises: a) comparing an input signal with a
signal determined by a quadrant to which the input signal belongs,
and detecting imbalances between I and Q components with respect to
the input signal; and b) using the imbalances detected in a) to
correct the input signal. The present invention prevents distorting
of the demodulator's performance caused by the imbalances to
between I and Q components and increases application to high-speed
wireless communication.
Inventors: |
Song; Yun-Jeong (Daejeon,
KR), Kim; Young-Wan (Daejeon, KR), Kim;
Nae-Soo (Daejeon, KR), Lee; Ho-Jin (Daejeon,
KR) |
Assignee: |
Electronics and Telecommunications
Research Institute (Daejeon, KR)
|
Family
ID: |
19717045 |
Appl.
No.: |
10/136,307 |
Filed: |
May 2, 2002 |
Foreign Application Priority Data
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Dec 14, 2001 [KR] |
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2001-79319 |
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Current U.S.
Class: |
375/316; 375/326;
375/340; 375/329 |
Current CPC
Class: |
H04L
27/3863 (20130101); H04L 2027/0016 (20130101); H04L
2027/0024 (20130101) |
Current International
Class: |
H04L
27/38 (20060101); H04L 27/00 (20060101); H04L
027/22 (); H04L 027/06 (); H04L 027/14 () |
Field of
Search: |
;375/316,317,261,279,280,340,326,324,345,329 ;329/329 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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001363391 |
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Nov 2003 |
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EP |
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06-188938 |
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Jul 1994 |
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JP |
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Primary Examiner: Bocure; Tesfaldet
Attorney, Agent or Firm: Mayer, Brown, Rowe & Maw
LLP
Claims
What is claimed is:
1. A method for detecting and correcting amplitude and phase
imbalances between in-phase (I) and quadrature-phase (Q) components
in a high-speed wireless communication quadrature demodulator,
comprising: a) comparing an input signal with a signal determined
by a quadrant to which the input signal belongs, and detecting
imbalances between I and Q components with respect to the input
signal; and b) using the imbalances detected in a) to correct the
input signal, wherein a) comprises: 1) determining a quadrant
position of the input signal; 2) using the quadrant position
determined in 1) to determine the input signal with respect to
respective quadrants; 3) respectively determining the signals
determined with respect to respective quadrants in 2); 4)
subtracting the determined signals in 3) from the determined
signals in 2); and 5) averaging the respective subtracted signals
to output the amplitude and phase imbalances between I and Q
components.
2. A method for detecting and correcting amplitude and phase
imbalances between in-phase (I) and quadrature-phase (Q) components
in a high-speed wireless communication quadrature demodulator
comprising: a) comparing an input signal with a signal determined
by a quadrant to which the input signal belongs, and detecting
imbalances between I and Q components with respect to the input
signal; and b) using the imbalances detected in a) to correct the
input signal, wherein b) comprises: 1) delaying the input signal by
one symbol; 2) determining the input signal's quadrant position; 3)
determining the amplitude and phase imbalance signals between I and
Q components detected with respect to the input signal according to
the quadrant position determined in 2); and 4) subtracting the
imbalance signals determined in 3) from the input signal delayed in
1) to correct the input signal.
3. A quadrature demodulator for high-speed wireless communication,
comprising: a multiplier for performing carrier frequency offset
correction and signal magnitude correction on signals received
through an antenna; an amplitude and phase imbalance corrector for
correcting the amplitude and phase imbalances of the signals output
from the multiplier, and outputting them; a carrier phase detector
for detecting a phase of the carrier from the signals output from
the amplitude and phase imbalance corrector; an amplitude and phase
imbalance detector for comparing the signals output from the
carrier phase detector with the signals determined by the quadrant
to which the signals belong, detecting the amplitude and phase
imbalances of the signals between I and Q components, and
outputting them to the amplitude and phase imbalance corrector; and
a symbol decision unit for extracting symbol values from the
signals output from the carrier phase detector, and outputting
them, wherein the amplitude and phase imbalance corrector
comprises: a signal delay unit for delaying the signal input from
the multiplier by one symbol; a quadrant decision unit for
determining a position of the quadrant corresponding to the input
signal; a multiplexer for comparing the input signal with the
signal determined by the quadrant to which the input signal
belongs, matching the amplitude and phase imbalance of the detected
input signal between the I and Q components with the quadrant
position determined by the quadrant decision unit, and outputting
results; and a subtractor for subtracting the signal output from
the multiplexer from the signal output from the signal delay unit,
and outputting results.
4. A quadrature demodulator for high-speed wireless communication
comprising: a multiplier for performing carrier frequency offset
correction and signal magnitude correction on signals received
through an antenna; an amplitude and phase imbalance corrector for
correcting the amplitude and phase imbalances of the signals output
from the multiplier, and outputting them; a carrier phase detector
for detecting a phase of the carrier from the signals output from
the amplitude and phase imbalance corrector; an amplitude and phase
imbalance detector for comparing the signals output from the
carrier phase detector with the signals determined by the quadrant
to which the signals belong, detecting the amplitude and phase
imbalances of the signals between I and Q components, and
outputting them to the amplitude and phase imbalance corrector; and
a symbol decision unit for extracting symbol values from the
signals output from the carrier phase detector, and outputting
them, wherein the amplitude and phase imbalance detector comprises:
a quadrant decision unit for receiving an input signal from the
carrier phase detector and outputting a corresponding quadrant
position; a demultiplexer for outputting the input signal to be
matched with the quadrant position output by the quadrant decision
unit; a signal decision unit for outputting a signal determined
with respect to the quadrant corresponding to the signal output
from the demultiplexer; a subtractor for subtracting the signal
output from the signal decision unit from the signal output from
the demultiplexer, and outputting results; and a signal averager
for averaging the signals output from the subtractor, and
outputting results.
5. A quadrature demodulator for high-speed wireless communication,
comprising: a multiplier for performing carrier frequency offset
correction and signal magnitude correction on signals received
through an antenna; an amplitude and phase imbalance corrector for
correcting the amplitude and phase imbalances of the signals output
from the multiplier, and outputting them; a carrier phase detector
for detecting a phase of the carrier from the signals output from
the amplitude and phase imbalance corrector; an amplitude and phase
imbalance detector for comparing the signals output from the
carrier phase detector with the signals determined by the quadrant
to which the signals belong, detecting the amplitude and phase
imbalances of the signals between I and Q components, and
outputting them to the amplitude and phase imbalance corrector; and
a symbol decision unit for extracting symbol values from the
signals output from the carrier phase detector, and outputting
them, wherein the signal averager is a low pass filter for
filtering low frequency ranges of the signal output from the
subtractor, and outputting results.
Description
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a quadrature demodulator used for
a high-speed wireless communication system. More specifically, the
present invention relates to a method for detecting and correcting
amplitude and phase imbalances between I and Q components of
complex signals generated by a quadrature demodulator
(b) Description of the Related Art
In a high-speed wireless communication system, the demodulator
receives signals through an antenna, a radio frequency (RF) unit,
and an intermediate frequency (IF) unit. The RF unit and IF unit
convert the high frequency to a low frequency and amplifies the
signals to generate desired signals.
The RF unit and the IF unit utilize various analog elements
including mixers and amplifiers that satisfy specifications within
a certain range, but the specifications have some limits, and input
signals are distorted by incompleteness of isolation and phase
orthogonal properties between the elements.
Distortion factors include amplitude and phase imbalances between
in-phase (I) and quadrature-phase (Q) components at the quadrature
demodulator, in, e.g., QPSK and/or QAM demodulators. The amplitude
and phase imbalances between I-phase and Q-phase components cause
degradation of the performance of the demodulator in the modem for
recovering signals. Therefore, methods for removing the amplitude
and phase imbalances between the I and Q components are
required.
Regarding removal of the amplitude and phase imbalances between I
and Q components, several methods using an RF direct conversion
receiver are disclosed. The U.S. Pat. No. 6,044,112 entitled
"Method and apparatus for correcting amplitude and phase imbalances
in demodulators" by Joshua L. Koslov dated Mar. 28, 2000 discloses
a method for providing several complex adders and multipliers as
well as a counter to the demodulator to correct gain and phase
imbalances. However, the method by Koslov increases implementation
complexity by using complex multipliers and is sensitive to noise
because it utilizes a simple counter at the demodulator. Further,
since this method sets the amplitude and phase imbalances between I
and Q components according to counter step, its response speed
depends on the increase and decrease step size of the count. The
method does not reflect the actual received signal, but depends on
counter step size.
In addition, the U.S. Pat. No. 5,949,821 entitled "Method and
apparatus for correcting phase and gain imbalances between
in-phase(I) and quadrature (Q) components of a received signal
based on a determination of peak amplitudes" by Shahriar Emami
discloses a method for detecting amplitude peak values of
demodulated I and Q components, and correcting the amplitude and
phase imbalances between I and Q components using the peak values.
The patent sets one of the I and Q components as a reference
component and another one as an imbalance component, finds the
amplitude peak value of each component, and finds the phase
imbalance using sine functions. It uses arcsine functions to
determine the phase imbalances between I and Q components, but this
application of the arcsine functions increases digital circuit
complexity or degrades the system's performance.
The above-noted patents have failed to solve the problems of
circuit implementation complexity and noise sensitivity, so an
improved method of detecting and correcting the amplitude and phase
imbalances between I and Q components is now required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for
detecting and correcting amplitude and phase imbalances between I
and Q components.
In one aspect of the present invention, a method for detecting and
correcting amplitude and phase imbalances between in-phase (I) and
quadrature (Q) components in a high-speed wireless, communication
quadrature demodulator, comprises: a) comparing an input signal
with a signal determined by a quadrant to which the input signal
belongs, and detecting imbalances between I and Q components with
respect to the input signal; and b) using the imbalances detected
in a) to correct the input signal.
The step a) comprises: 1) determining a quadrant position of the
input signal; 2) using the quadrant position determined in 1) to
determine the input signal with respect to respective quadrants; 3)
respectively determining the signals determined with respect to
respective quadrants in 2); 4) subtracting the determined signals
in 3) from the determined signals in 2); and 5) averaging the
respective subtracted signals to output the amplitude and phase
imbalances between I and Q components.
The step b) comprises: 1) delaying the input signal by one symbol;
2) determining the input signal's quadrant position; 3) determining
the amplitude and phase imbalance signals between I and Q
components detected with respect to the input signal according to
the quadrant position determined in 2); and 4) subtracting the
imbalance signals determined in 3) from the input signal delayed in
1) to correct the input signal.
The amplitude and phase imbalance corrector comprises: a signal
delay unit for delaying the signal input from the multiplier by one
symbol; a quadrant decision unit for determining a position of the
quadrant corresponding to the input signal; a multiplexer for
comparing the input signal with the signal determined by the
quadrant to which the input signal belongs, matching the amplitude
and phase imbalance of the detected input signal between I and Q
components with the quadrant position determined by the quadrant
decision unit, and outputting results; and a subtractor for
subtracting the signal output from the multiplexer from the signal
output from the signal delay unit, and outputting results.
The amplitude and phase imbalance detector comprises: a quadrant
decision unit for receiving an input signal from the carrier phase
detector, and outputting the corresponding quadrant position; a
demultiplexer for demultiplexing the input signal to be matched
with the quadrant position output by the quadrant decision unit; a
signal decision unit for outputting a signal determined with
respect to the quadrant corresponding to the signal output from the
demultiplexer; a subtractor for subtracting the signal output from
the signal decision unit from the signal output of the
demultiplexer, and outputting results; and a signal averager for
averaging the signals output from the subtractor, and in outputting
results.
The signal averager is a low pass filter for filtering low
frequency ranges of the signal output from the subtractor, and
outputting results.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate an embodiment of the
invention, and, together with the description, serve to explain the
principles of the invention:
FIG. 1 shows a block diagram of a quadrature demodulation receiver
for implementation of detecting and correcting amplitude and phase
imbalances between I and Q components according to a preferred
embodiment of the present invention;
FIG. 2 shows an I-Q constellation diagram for displaying the
amplitude and phase imbalances between I and Q components;
FIG. 3 shows a detailed block diagram of an I-Q imbalance detector
in the quadrature demodulation receiver of FIG. 1; and
FIG. 4 shows a detailed block diagram of an I-Q imbalance corrector
in the quadrature demodulation receiver of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following detailed description, only the preferred
embodiment of the invention has been shown and described, simply by
way of illustration of the best mode contemplated by the
inventor(s) of carrying out the invention. As will be realized, the
invention is capable of modification in various obvious respects,
all without departing from the invention. Accordingly, the drawings
and description are to be regarded as illustrative in nature, and
not restrictive.
FIG. 1 shows a block diagram of a quadrature demodulation receiver
for implementation of detecting and correcting amplitude and phase
imbalances between I and Q components according to a preferred
embodiment of the present invention.
As shown, the quadrature demodulation receiver comprises: complex
multipliers 101 and 102; an analog-digital (A/D) converter 103; a
matched filter 104; an I-Q imbalance corrector 105; a carrier phase
detector 106; a decision unit 107; an automatic gain controller
(AGC) 108; a carrier phase recovery unit 109; an I-Q imbalance
detector 110; an automatic frequency controller (AFC) 111; and a
symbol timing recovery unit 112.
The quadrature demodulation receiver receives signals through an
antenna, an RF unit, and an IF unit (not illustrated), and provides
them to a quadrature converter (not illustrated) to generate
complex signals (receiving signals). The first complex multiplier
101 corrects carrier frequency offset by control of the AFC 111,
and the second complex multiplier 102 controls the input signal's
gain with the AGC 108.
The above-generated signals are provided to the A/D converter 103
so as to be converted to digital signals.
The A/D converted signals are provided to the matched filter 104
and then to the I-Q imbalance corrector 105. The A/D converter 103
receives a control signal from the symbol timing recovery unit 112,
and determines a sampling position of the A/D converter 103.
The signals output from the I-Q imbalance corrector 105 are
recovered to signal carrier through the carrier phase detector 106
and the carrier phase recovery unit 109.
The decision unit 107 receives the recovered signals and determines
signals to extract symbol values. The I-Q imbalance detector 110
detects the amplitude and phase imbalances using the recovered
signals, and the I-Q imbalance corrector 105 corrects the
imbalances according to detection results.
FIG. 2 shows an exemplary I-Q constellation after signal recovery
when imbalances exist between I and Q components. In this instance,
the black dots represent desired positions of recovered signals,
and the white dots indicate the signals caused by the imbalances
between I and a components.
FIGS. 2(a) and 2(b) show the phase imbalances of the Q components
with respect to the I components, and FIGS. 2(c) and 2 (d)
represent the phase imbalances of the I components with respect to
the Q components.
FIG. 3 shows a detailed block diagram of the I-Q imbalance detector
110 in the quadrature demodulation receiver of FIG. 1.
As shown, the I-Q imbalance detector 110 comprises: a quadrant
decision unit 301; a demultiplexer 302; signal decision units 303,
304, 305, and 306; subtractors 307, 308, 309, and 310; and low pass
filters (LPFs) 311, 312, 313, and 314.
The quadrant decision unit 301 uses the carrier phase detector 106
of FIG. 1 and the carrier phase recovery unit 109 of FIG. 1 to
determine a quadrant of the recovered carrier that is concurrently
input to the demultiplexer 302 and determined into the respective
quadrants.
The signals determined into the respective quadrants are input to
the signal decision units 303, 304, 305, and 306 to be determined.
The signals decided into the respective quadrants and the
determined signals are input to the subtractors 307, 308, 309, and
310 so as to subtract the determined signals from the decided
signals.
The subtracted signals are input to the respective LPFs 311, 312,
313, and 314 to be averaged. Table 1 represents output values from
the quadrant decision unit.
TABLE 1 I Q SEL I > 0 Q > 0 00 I < 0 Q > 0 01 I > 0
Q < 0 10 I < 0 Q < 0 11
As shown in FIG. 2, the LPFed signals are used for detecting
imbalance states between I and Q components in the respective
quadrants. The detected imbalance states are used for correcting
the imbalances at the I-Q imbalance corrector of FIG. 4.
FIG. 4 shows a detailed block diagram of an I-Q imbalance corrector
in the quadrature demodulation receiver of FIG. 1.
As shown, the I-Q imbalance corrector comprises: a quadrant
decision unit 401; one symbol delay unit 402; a multiplexer 403;
and a subtractor 404.
The quadrant decision unit 401 determines the quadrant position of
the complex signal output from the matched filter 104 of FIG. 1.
Concurrently, the complex signal is input to the symbol delay unit
402 to be delayed by one symbol.
The signal SEL, which controls the multiplexer output, is input to
the multiplexer 403; and the signals averaged through the
respective LPFs in the I-Q imbalance detector 110 of FIG. 3 are
concurrently input to the multiplexer 403, and output signals are
determined according to determination results of the quadrant
positions.
The signal delayed by one symbol by the symbol delay unit 402 is
input to the subtractor 404, and a subtracted symbol is output
according to a signal input from the multiplexer 403.
The present invention enables detection of the imbalances between
the I and Q components generated in the quadrature demodulator and
correction thereof, thereby preventing distortion of the
demodulator's performance caused by the imbalances between I and Q
components.
Also, differing from the conventional I and 0 imbalance correctors,
the present invention uses LPFs for detecting complex signals and
removing noise of the detected signals to reduce noise effects, and
corrects the imbalances between I and Q components without
detecting the phase imbalances between I and Q components, thereby
increasing application to high-speed wireless communication.
While this invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not
limited to the disclosed embodiments, but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *